1. Field of Invention
The invention relates to a wire cut electric discharge machine where a wire electrode is moved relative to a workpiece so as to machine the workpiece using an electric discharge. In particular, the invention relates to a control apparatus that controls the wire cut electric discharge machine, a method of controlling the wire cut electric discharge machine, and a storage medium to execute the method.
2. Description of Related Art
There are various wire cut electric discharge machines that give a workpiece electric discharge machining by moving a wire electrode relative to the workpiece. FIG. 6 shows an explanatory drawing of a wire cut electric discharge machine. As shown in FIG. 6, in the wire cut electric discharge machine, a machine table 1 supporting a workpiece W is moved freely on an XY plane by a XY drive mechanism 2. An upper wire guide 3 is disposed at an upper portion of the workpiece W, and a lower wire guide 4 is disposed securely at a lower portion of the workpiece W. A wire 5 is provided so as to hang across the upper wire guide 3 and the lower wire guide 4 with a predetermined tension, created by a wire drive mechanism, not shown.
The upper wire guide 3 is moved freely on a UV plane, which is parallel to the XY plane, by a UV drive mechanism 6. Thus, if the XY drive mechanism 2 is activated under the condition that the upper wire guide 3 is secured immediately above the lower wire guide 4, machining can be given to the workpiece W along a vertical plane. If the upper wire guide 3 is shifted from the top of the lower wire guide 4, tapering can be given to the workpiece W.
During a normal machining, if a workpiece is machined along a contour WG, i.e., an outline of the workpiece, as shown in FIG. 7, for example, drive mechanisms 2, 6 are controlled so as to move the center of the wire 5 along a movement path K which is away from the contour WG for a predetermined offset (a discharge gap of the wire 5+a radius of the wire 5). In Japanese Laid-Open Patent Publication No. 60-108219, when a corner of the contour WG is machined, a correction block, which does not correspond to the contour WG, is inserted in the movement path K. Machining accuracy is increased and machining time is reduced at corners because needless movement is omitted from the corners.
The discharge gap is the distance at which the discharge is generated between the wire electrode and the workpiece. The wire electrode applies an electrical discharge to the workpiece from a distance of the discharge gap. The discharge gap varies according to the machining condition, such as voltage. The higher the voltage is, the larger the discharge gap becomes. The lower the voltage is, the smaller the discharge gap becomes. Generally, the discharge gap is larger for rough machining, and smaller for fine machining.
In the Numerical Control program, a block is a unit of movement along the movement path where the wire electrode is moved to machine a workpiece. One command corresponds to one block. There is a straight block whose path is straight, and an arc block whose path is arced. A corner is a joint between blocks. Therefore, a workpiece may be machined into an angular shape at the corner.
On the corner, voltage to be applied to the wire electrode may be changed. In other words, the voltage may be changed at the corner in accordance with changes of a taper angle of the workpiece and a degree of the machining fluid that is sprayed into the workpiece. Because the discharge gap varies as the voltage changes, the shape of the workpiece W, to be obtained, may differ when the voltage is changed at the start point of the correction block and when the voltage is changed at the end point of the correction block. Furthermore, the workpiece W might not be machined into a desired shape.
The invention provides a control apparatus for a wire cut electric discharge machine capable of changing a machining condition, such as a voltage to be applied to the wire electrode, which entails a change of a discharge gap of the wire electrode, to cause the machine to machine the workpiece into a desired shape by setting a position to change the machining condition appropriately; a method of controlling the wire cut electric discharge machine; and a storage medium to execute the method.
In an exemplary aspect of the invention, a control apparatus that controls a wire cut electric discharge machine having an electrode moving device that moves a wire electrode relative to a workpiece, may include a machining condition changing device that changes a machining condition entailing a change of a discharge gap generated by the wire electrode, a correction block inserting device that inserts a correction block into a corner of a movement path where the wire electrode is moved by the electrode moving device, the correction block not corresponding to the contour of the workpiece to be machined, and a changing position setting device that sets a changing position to change the machining condition on the correction block when the machining condition changing device needs to change the machining condition before and after the corner.
In the wire cut electric discharge machine, the wire electrode is moved relative to a workpiece to be machined by the electrode moving device, so that the workpiece can be machined into a desired shape, and the machining condition that entails the change of the discharge gap generated by the wire electrode can be changed by the machining condition changing device.
In the control apparatus, a correction block that does not correspond to the contour of the workpiece can be inserted in the corner of the movement path where the wire electrode is moved by the electrode moving device. When it is necessary to change the machining condition before and after the corner, the position change setting device sets the position to change the machining condition on the correction block.
In other words, when the correction block is not inserted, the changing position to change the machining condition is inevitably determined to a position corresponding to the corner. However, when the correction block is inserted, the changing position is set on the correction block. Thus, if the machining condition that entails the change of the discharge gap is changed, the wire cut electric discharge machine can be controlled so as to machine the workpiece into a desired shape.
In another exemplary aspect of the invention, the changing position setting device may automatically set the changing position to a position where a rim of the wire electrode is away from the contour of the workpiece to be machined by a distance equal to or greater than either of the discharge gaps set before and after the machining condition is changed, whichever is larger.
When the rim of the wire electrode is away from the contour of the workpiece to be machined by a distance equal to or greater than either of the discharge gaps set before and after the machining condition is changed, whichever is larger, if the machining condition is changed at the position, the contour of the workpiece is unaffected. The changing position change setting device automatically sets the changing position to change the machining condition in such a position. As the changing position is set as mentioned above, the wire cut electric discharge machine can be controlled so as to machine workpiece into a desired shape more reliably. As the changing position is set automatically, the operationality of the wire cut electric discharge machine can be further improved.
In a further exemplary aspect of the invention, the changing position setting device may set the changing position only when a change of the machining condition entails a change of the discharge gap.
Even though the machining condition is changed during an electric discharge machining of a workpiece, as long as the discharge gap is not changed, the contour of the workpiece is unaffected. The changing position to change the machining condition is set only when the change of the machining condition entails the change of the discharge gap. Therefore, redundant processes are omitted, so that the entire control process can be performed faster.